The present invention relates generally to transmissions having multiple power paths, and, more particularly, to such transmissions in which a balance is effected between the power transmitted by and between the various paths so as to evenly distribute loads therebetween.
1. Field of the Invention
Inherent in multiple power path geared transmissions is an imbalance in the power to be transmitted through each path. Fault lies not in the design, but in the manufacture.
There are practical limits on the manufacturing tolerances that can be achieved before costs accelerate and greatly exceed the benefits to be realized. Such tolerances may result in variations in gear diameter, root diameter, pitch circle diameter, and even tooth shape, depending on the hobbing device.
Efforts to balance the loading between power paths have been ongoing since at least the very early 1900""s when transmissions were used to drive multiple screws on ocean going vessels. As transmissions evolved, they became smaller in size, but carried ever increasing loads, thereby making multiple paths more imperative and the balancing of loading among such paths essential.
2. Overview of the Prior Art
While there are myriad theories on the most effective approach to balancing loading between multiple paths in geared transmissions, most recently, advantageous use of the inherent characteristics of helical gears to respond to torsional loading by the creation of a force vector which is co planer with the axis of rotation of the gear. More specifically, by permitting helical gears limited axial movement on their respective shafts, allows those gears to respond to such force vector by axial movement to arrive at a balance between power paths. My recently issued U.S. Pat. No. 5,927,147 is exemplary of this group of prior art efforts.
Reference is also made to Matthews U.S. Pat. No. 2,899,822 for a recognition of, and interesting exploration of, the theory of the proportionate relationship between torque and power transmitted in a helical gear transmission.
Others have explored other avenues and have determined, for example, that flexible gearing, or flexible mounting of gears, is a means of accomplishing balance between multiple power paths, and exemplary of this group of U.S. Pat. Nos. 1,502,199 and 1,591,826 to Hodgkinson, and U.S. Pat. No. 1,320,459 to Edwards. Still others opine that permitting limited movement of the quill, or jack shaft itself, is the solution, and evolving from that concept is, among others, U.S. Pat. No. 4,266,436 to Reppert.
Eggins U.S. Pat. No. 3,545,296 is of interest in that it uses a flexible diaphragm to control the spacing between halves of a split gear.
A significant number of transmissions attempt to take advantage of these principals, as well as others, including the simplistic use of basic laws of physics relating to action and reaction to the application of forces between gears, and particularly helical gears, all in an effort to balance loading and, with it, wear in multi path geared transmissions.
Finally, there is a line of patents in which advantageous use of the relationship between fluid pressure and power transmitted is embodied in a geared transmission. Interestingly, these patents seem to focus on the aircraft industry. For example, in Taylor U.S. Pat. No. 2,386,367 layshafts are subjected to fluid under pressure delivered to an end of each by a pump so as to displace the shaft by an amount sufficient to deliver the desired power. The Matthews ""822 patent, referenced above, has a similar vision, employing pump 56 to create pressure.
In Parenti U.S. Pat. No. 3,648,533, a spring loaded piston behind each shaft creates pressure, and Marchand Pat. No. 3,034,369 is similar in concept. There is an area of commonality among these patents, and that is that a system for creating the desired positive operating pressure is in place to develope the desired pressure/load ration, which is distinguishable from the present invention in which a passive system simply equalizes pressure among the several load carrying paths.
The geared transmission of the present invention is characterized by multiple power paths, which power paths are in communication with one another via a discrete fluid path. The fluid is sensitive to imbalance in the loading on the various power paths and, via the communication between them, effects an appropriate balance.
Accordingly, it is an objective of the present invention to effect a balance of loads on the various power paths which comprise a geared transmission. It is an objective of the present invention, incident to the foregoing, to effect balanced loading in a smooth, yet rapid manner.
Another objective of the present invention is to accomplish balanced loading between and among various power paths in an exceedingly efficient and economical manner, and a related objective is to accomplish the foregoing in a fashion which minimizes wear and damage to the geared components of the transmission.
Another and still further objective is to create a passive fluid environment in which increases in forces on one power path are sensed and balanced with companion power paths.